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A123088
a(1)=1. For n>=2, a(n) = n + (largest integer which is <= n and is missing from the earlier terms of the sequence).
2
1, 4, 6, 7, 10, 11, 12, 16, 18, 19, 20, 21, 26, 28, 30, 31, 34, 35, 36, 37, 38, 44, 46, 48, 50, 51, 54, 55, 58, 59, 60, 64, 66, 67, 68, 69, 70, 71, 78, 80, 82, 84, 86, 87, 90, 91, 94, 95, 98, 99, 100, 104, 106, 107, 108, 112, 114, 115, 116, 117, 122, 124, 126, 127, 130, 131
OFFSET
1,2
EXAMPLE
The largest integer which is <= 12 and does not occur among the first 11 terms of the sequence is 9. So a(12) = 12 + 9 = 21.
MATHEMATICA
f[l_List] := Block[{n = Length[l] + 1, k = n}, While[MemberQ[l, k], k-- ]; Append[l, n + k]]; Nest[f, {1}, 70] (* Ray Chandler, Sep 30 2006 *)
PROG
(PARI) {my(m=66, w=vector(2*m), a); print1(a=1, ", "); for(n=2, m, my(k=n); while(w[k], k--); print1(a=n+k, ", "); w[a]=1)} \\ Klaus Brockhaus, Oct 05 2006
CROSSREFS
Cf. A123679.
Sequence in context: A340847 A286494 A086170 * A256657 A189085 A153235
KEYWORD
nonn
AUTHOR
Leroy Quet, Sep 27 2006
EXTENSIONS
Extended by Ray Chandler and Klaus Brockhaus, Sep 30 2006
STATUS
approved